1. Field of the Invention
This invention relates to tablet excipients that provide a cushioning effect for preserving the physical integrity of other components of the tablet. More specifically, the invention relates to granules including porous microcrystalline cellulose that cushion controlled release particles during tableting, tablets containing such porous microcrystalline cellulose granules and methods for making such granules and tablets.
2. Description of the Prior Art
Controlled release particles containing an active ingredient for pharmaceutical or veterinary products have been employed in a variety of different delivery forms, such as sprinkles or capsules. For various reasons, it has become desirable to incorporate such controlled release particles into tablets made using a compression step to form the tablet. However, such controlled release particles are relatively fragile and thus may become damaged during the compression step of tableting thereby significantly altering the release rate of the active ingredients from the controlled release particles. There are some commercial products that contain controlled release particles in a tablet form. For example, Theo-dur® is a tablet form of controlled release particles of theophylline contained in a wax matrix. Also, the popular drug Prilosec® is sold in the form of tablets that include controlled release particles therein.
Currently, microcrystalline cellulose (“MCC”), for example, Avicel® PH grades, is widely utilized in the preparation of pharmaceutical and veterinary tablets, primarily as a compression aid and binder, and, secondarily, as a disintegrant. Different grades of MCC provide different degrees of compressibility, but none is capable of sufficiently protecting the physical integrity of other components in the tablet, particularly controlled release particles, granules, or spheres during the compression step of tableting. The damage that occurs to such controlled release particles during the compression step of the tableting process may be measured by the increased rate at which the active ingredient is released from the tablet after compression as compared to the release rate for the controlled release particles prior to compression. It is believed that one factor which may contribute to the increased release rate is that the fragile, controlled release coating on the outer surface of the controlled release particles can crack during the compression step of the tableting process.